1. Field of the Invention
The present invention relates to a three-dimensional (3D) image/two-dimensional (2D) image switching display apparatus which can display a 3D image and a 2D image, switching them from one to the other, and a portable terminal device incorporating the 3D image/2D image switching display apparatus.
2. Description of the Related Art
Display apparatuses capable of displaying 3D images have been developed. 3D image display systems that have been studied so far can be classified into a type which uses glasses and a type which does not. With the use of the glasses-using type which includes an anaglyph type and a polarization glass type using polarization, a user cannot substantially avoid wearing glasses. In this respect, recently active studies have been made on glass-less 3D image display apparatuses which do not use glasses.
Glass-less 3D image display apparatuses include a parallax barrier type and a lenticular lens type. The parallax barrier type was conceived by Berthier in 1896 and verified by Ives in 1903. The parallax barrier has multiple thin vertical openings or slits formed therein. In the vicinity of the parallax barrier are laid out pixels for a right eye (hereinafter referred to as “right-eye pixels”) and pixels for a left eye (hereinafter referred to as “left-eye pixels”) in a direction perpendicular to the lengthwise direction of the slits. Lights from the pixels are partly shielded when passing the parallax barrier. Specifically, the pixels are laid out in such a way that while lights from the left-eye pixels reach the left eye but are shielded from going toward the right-eye pixels, lights from the right-eye pixels reach the right eye but do not reach the left eye. Accordingly, the lights from the left-eye pixels and the lights from the right-eye pixels respectively reach the left and right eyes, thus allowing the user to identify the image as a 3D image. At the time the parallax barrier was devised, the parallax barrier was arranged between the pixels and eyes and was therefore eyesore and provided a low visibility. The recent achievement of liquid crystal displays has made it possible to arrange the parallax barrier at the back of each display, improving the visibility. This has resulted in active studies on parallax barrier type display apparatuses at present.
The lenticular lens type display apparatus was invented in around 1910 by Ives et al. mentioned above, as described in, for example, “3D Display by Chihiro Masuda from Sangyo Tosho Publishing Co., Ltd. FIG. 1 is a perspective view showing the shape of a lenticular lens. As shown in FIG. 1, a lenticular lens 100 has two sides, one being flat and the other having a plurality of semicylindrical projections (cylindrical lenses) formed thereon extending in one direction. Right-eye pixels which display an image for the right eye and left-eye pixels which display an image for the left eye are alternately laid out on the focal plane of the lens. Therefore, light from each pixel is distributed by the lenticular lens 100 to directions respectively going to the right and left eyes. This can allow the right and left eyes to identify different images so that the observer can recognize a 3D image. This lenticular lens type is widely adapted to stereoscopic TVs or the like at present.
Recently have active studies also been made to permit a 3D image display apparatus to display a 2D image. The easiest scheme is to make the aforementioned images for the right eye and for the right eye match with each other and display the same image. In this case, the same information should be displayed over two pixels, thus reducing the resolution to a half. This particularly raises a significantly problem that the visibility of texts characters which are used most frequently at the time of displaying a 2D image drops significantly.
Studies have so far been made on schemes of displaying a 3D image and a 2D image, switching them from one to the other, without reducing the resolution. For example, Japanese Patent Publication Laid-Open No. 068961/1996 and Japanese Patent Publication Laid-Open No. 112273/1992 describe a 3D image display apparatus using a lenticular lens, which is designed in such a way that between the lenticular lens and a transparent plate so arranged as to face the irregular side of the lenticular lens, a substance having the same refractive index as the material for the lenticular lens is injected to nullify the lens effect. FIG. 2 is a perspective view showing the conventional 3D image display apparatus. As shown in FIG. 2, a transparent plate 103 is laid on the upheaval side of a lenticular lens 102 of this conventional 3D image display apparatus 101 and a clearance 104 is made between the lenticular lens 102 and the transparent plate 103. At the time of displaying a 2D image, a liquid substance (not shown) having the same refractive index as the lens is injected into the clearance 104 by a pump 105 or the like. This disables the lens effect and can thus ensure 2D display. In case of displaying a 3D image, the injected substance is discharged from the clearance 104 to make the lens effect available, thereby ensuring 3D display.
Japanese Patent Publication Laid-Open No. 197343/1997 describes a 3D image display apparatus which switches between the display of a 3D image and the display of a 2D image by changing the distance between the image display surface of a pixel and the lenticular lens. FIG. 3 is a cross-sectional view showing this conventional 3D image display apparatus. In the conventional 3D image display apparatus 111, as shown in FIG. 3, the distance between a lenticular lens 112 and an image display unit 113 is variable. Right-eye pixels 114 and left-eye pixels 115 are alternately laid out on the image display unit 113. When the distance between the lenticular lens 112 and the image display unit 113 is set to the focal distance of the lenticular lens, the lens effect of the lenticular lens 112 becomes effective with respect to lights from the pixels 114 and 115, thereby ensuring the display of a 3D image. When the distance between the lenticular lens 112 and the image display unit 113 is set to approximately zero, on the other hand, the lens effect of the lenticular lens 112 is disabled so that a 2D image can be displayed. In case where an electronic display, such as a liquid crystal device, is used as the image display unit 113, the thickness of the glass substrate limits the distance to be variable, thus making it difficult to set the distance between the lenticular lens 112 and the image display unit 113 is set to approximately zero. To cope with this difficulty, image transfer means, such as a fiber face plate 116, is provided on the lenticular-lens side surface of the image display unit 113 to equivalently cause the lenticular lens 112 to come close to the vicinity of the image display unit 113.
The prior art however has the following problems. The conventional 3D image/2D image switching display apparatus is provided with a lenticular lens and displays a 3D image by enabling the lens effect of the lenticular lens and displays a 2D image by disabling the lens effect of the lenticular lens. As switching means to switch between enabling and disabling of the lens effect of the lenticular lens is large in scale, the 3D image/2D image switching display apparatus disadvantageously becomes thicker and larger. The existence of the switching means reduces the display quality. Further, the operation of the switching means takes times, resulting in a longer time needed to switch between the display of a 3D image and the display of a 2D image. Furthermore, the provision of the switching means increases the cost for the 3D image/2D image switching display apparatus.
Those problems will be discussed more specifically. According to the prior art described in Japanese Patent Publication Laid-Open No. 068961/1996 and Japanese Patent Publication Laid-Open No. 112273/1992 as shown in FIG. 2, a mechanism which injects and discharges a liquid substance having the same refractive index as the material for the lenticular lens 102 into and from the clearance 104 by means of the pump 105 is provided as the switching means to enable/disable the lens effect of the lenticular lens. This method however requires the pump 105 to inject and discharge the liquid substance and a tank to store the discharged liquid substance. The requirements inevitably enlarge the apparatus and increase the cost. If the injection and discharge of the liquid substance are not done completely, bubbles or the like are produced, thereby reducing the display quality. In addition, the injection and discharge of the liquid substance take time, resulting in a longer time to switch the display of 2D and 3D images from one to another.
According to the prior art described in Japanese Patent Publication Laid-Open No. 197343/1997 as shown in FIG. 3, a mechanism which changes the distance between the lenticular lens 112 and the image display unit 113 is provided as the switching means to enable/disable the lens effect of the lenticular lens. This structure needs space for changing the distance and thus increases the thickness of the 3D image/2D image switching display apparatus. The need to use the expensive fiber face plate 116 or the like leads to a cost increase. Further, as light from the image display unit 113 passes through the fiber face plate 116, the display quality becomes lower as compared with the case where the fiber face plate 116 is not provided. There is another problem that the movement of the lenticular lens 112 takes time.